mongoose/docs/c-api/net.h/mg_event_handler_t.md

title	decl_name	symbol_kind	signature
mg_event_handler_t	mg_event_handler_t	typedef	typedef void (*mg_event_handler_t)(struct mg_connection *, int ev, void *);

Callback function (event handler) prototype, must be defined by user. Mongoose calls event handler, passing events defined below.